1. Field of the Invention
The present invention relates, in general, to valves used in the commercial heating, refrigeration, and air conditioning industry, and in particular, to valves for precisely metering the flow of fluid therethrough.
2. Information Disclosure Statement
It is often desired to achieve constant flow control when dealing with a fluid used in any Heating, Ventilation & Air Conditioning (“HVAC”) application. Well-known solutions for this problem include the use of linear globe valves. A linear globe valve uses a multi-turn handwheel that operates a linear rising-stem control element, which closes onto a seating surface. A complex flow path through the valve, along with the linear rising-stem, allows the globe valve to possess important key features. One key feature is the high level of precision when throttling. Another key feature is the inherent rangeability, which is defined as the ratio of the maximum flow to the minimum controllable flow through the valve passage. Also, the inherent flow characteristics of the linear globe valve allows it to exhibit “equal percentage flow,” i.e., an inherent flow characteristic which, for equal increments of rated travel, will ideally yield equal percentage changes of the existing flow.
Unfortunately, some inherent disadvantages still remain with the linear globe valve design. One disadvantage with this type of valve is that it contains a contoured plug that works in conjunction with a metal seat. When the plug is pressed against the metal seat, there is no sealing surface to close against; thus there is wasted energy, or in this case leakage. Other recognized disadvantages with the linear globe valve design include a high pressure drop across the valve due to a restricted flow passage when the valve is fully open, and the need for a sufficient amount of space in order to open the valve, because it is controlled by a rising-stem. These undesirable factors must be taken into consideration when using this valve in any piping system.
In order to maintain all of the admirable performance characteristics of the linear globe valve without having to deal with considerably high-pressure losses, modified ball valves may be used in place of globe valves. FIG. 1 shows such a typical well-known conventional ball valve 20 having a threaded inlet port 22 and outlet port 24, each port having internal threads 26 of standard pitch and size for receiving similarly-threaded pipes (not shown) therewithin in a manner well-known to those skilled in the art. FIG. 9 shows another typical well-known conventional ball valve 2.20 having non-threaded inlet and outlet ports 2.22, 2.24 into which inlet and outlet pipes P are soldered in a manner well-known to those skilled in the art. Other than the threaded/non-threaded aspect of the ports, the prior art valves of FIGS. 1 and 9 are otherwise substantially the same, and a description of the valve of FIG. 1 will suffice for both, it being understood that similar structural features perform similar functions for both types of valves.
Well-known ball valve 20 includes a valve body 28, usually of a metal such as brass or stainless steel, a generally spherical ball 30, typically of a metal such as brass or chrome or stainless steel and having a transverse cylindrical bore 32 therethrough. Ball 30 is mounted for rotation with a metal stem 34, typically brass or stainless steel, about a vertical axis of stem 34 such that a 90° rotation of stem 34 about its axis causes ball valve 20 to go from a fully-closed position (shown in dotted outline) in which the cylindrical bore 32 of ball 30 is transverse to the axis of input and output ports 22, 24, to a fully-open position (shown in solid outline) in which the cylindrical bore 32 is aligned with the axis of input and output ports 22, 24. Stem 34 is typically mounted in a polytetrafluoroethylene (“PTFE”) polymer (often sold under the trademark TEFLON) stem bearing 36 within Namur mount 40 of like metal as valve body 28 for rotation of stem 34 with respect to valve body 28, and stem 34 may be sealed with a PTFE polymer stem seal 38 and one or more Viton O-rings 42. Typically, a well-known electrically-operated actuator (not shown) is coupled to stem 34 so as to cause the ball valve 20 to cycle between its open and closed positions in a manner well-known to those skilled in the art.
Pressure losses across these valves are small compared to those in globe valves. They exhibit excellent performance for on/off service, and the amount of shut-off leakage around the spherical control element of the ball valve is minimal, which allows for positive shut-off. Positive shut-off is referred to by the American National Standards Institute as a Class VI, “bubble tight” situation, which means that when the valve was tested under laboratory conditions with compressed air, no leakage was observed. Standard ball valves possess many excellent features, but do not exhibit desirable flow control. The advantage of using modified ball valves over the traditional style linear globe valves includes similar flow characteristics while making quarter-turn automation simple and economical.
Several different modified ball valves have been introduced to the valve industry in the last few years. A ball valve that uses a polymer insert to achieve equal percent flow characteristics is sold under the trademark OPTIMIZER by Griswold Controls, Inc., 2803 Barranca Pkwy, Irvine, Calif., and is described in a Griswold brochure entitled “HVAC Technology Review—Griswold Controls Introduces Optimized Temperature Control,” and in Mirandi, U.S. Pat. No. 5,937,890 (issued Aug. 17, 1999), fully included herein by reference. The Griswold OPTIMIZER ball valve insert is an insert that is press-fit into the spherical control element. It allows for multiple valve flow coefficient (Cν) selection for the user. The OPTIMIZER ball valve insert is designed for use in the manufacturer's valve only. Temperatures and pressures in the system must be limited due to the fact that the insert is made of a polymer material and could fail under certain conditions. Because of this problem, steam can not be used as the working fluid in the system. Fouling can also be a problem with the discs designed to yield smaller valve flow coefficient (Cν) values. With the narrow design of the parabolic shape of the orifice, small pieces of debris within the system could get trapped, disrupting the flow through the orifice and minimizing control. Due to the press fit design, the insert could become loose and potentially removed under high pressure.
Other attempts to address the poor control of a standard ball valve are ball valves with a disk insert sold under the trademark “Characterized Control Valves” and manufactured by Belimo Aircontrols (USA) Inc., 43 Old Ridgebury Road, Danbury, Conn. The disk insert is made of polytetrafluoroethylene (“PTFE”) polymer material, such as that sold under the trademark TEFLON, and is placed in the valve body upstream of the control element. The disk insert is held in place by the use of a retaining ring. Like the Optimizer, this control device can only be used in the manufacturer's valve. As with the Optimizer design, the PTFE insert could fail under high pressures and temperatures, the smaller parabolic orifice passages could become obstructed, and the insert could become loose and possibly removed under high pressure because of the simple retaining ring used to hold the insert in position. These Characterized Control Valves are described in a Belimo Aircontrols brochure entitled “The Difference is in the Details” and also are described in Carlson et al., U.S. Pat. No. 6,039,304 (issued Mar. 21, 2000), fully included herein by reference.
A ball valve that uses a one-piece lubricant-impregnated metal seat and is configured to provide a concave central surface portion that makes full-face direct sealing contact with the ball is sold by Worcester Controls Corporation, Marlboro, Mass., and is described in Reynolds et al., U.S. Pat. No. 5,074,522 (issued Dec. 24, 1991), fully included herein by reference. This design improves the flow control of a standard ball valve, but is an expensive alternative when compared with other designs in the industry. The Worcester valve is designed specifically for high pressure industrial applications, and is limited in regards to maximum Cν due to the specified geometry of the designed metal seats. When dealing with high pressure situations, the ball valve design must include very tight direct sealing contact between the spherical control element and the seats that are located adjacent the upstream and downstream sides of the valve within the valve housing. Due to the tight seal between the control element and the seats, the torque that is necessary to rotate the control element is greater than that found in a modified ball valve used in HVAC applications. In order to use automation to control the Worcester valve, expensive actuators would have to be used that have high torque capabilities. Fouling can also be a problem when a metal seat is used containing several small holes to regulate the flow. Debris can block several of the holes, changing the characteristics of the design, and limiting flow control
It is therefore desirable to have a flow control device that is intended to obviate problems of the types discussed above with respect to the Griswold, Belimo, and Worcester valve arrangement.
In addition to the Griswold Controls, the Belimo Aircontrols, and the Worcester Controls Corporation references mentioned above, the inventor also is aware of the following patent references, some of which may be relevant to the present invention: Wiley, U.S. Pat. No. 1,493,409, issued May 6, 1924; Hodgeman et al., U.S. Pat. No. 3,126,917, issued Mar. 31, 1964; Baumann, U.S. Pat. No. 4,085,774, issued Apr. 25, 1978;Ko, U.S. Pat. No. 4,903,725, issued Feb. 27, 1990; McEnearney, U.S. Pat. No. 4,960,260, issued Oct. 2, 1990; Yu, U.S. Pat. No. 5,123,628, issued Jun. 23, 1992; Schommer, U.S. Pat. No. 5,315,859, issued May 31, 2994; Gawlik, U.S. Pat. No. 5,655,571, issued Aug. 12, 1997; Sharp, U.S. Pat. No. 5,687,770, issued Nov. 18, 1997; and Lebo et al., U.S. Pat. No. 5,819,803, issued Oct. 13, 1998.
None of these references, either singly or in combination, are believed to disclose or suggest the present invention.